Robust telemetry repeater network system and method

ABSTRACT

A robust network telemetry repeater system exploits the repeater structure of data propagation and transmission and reception bi-directionality to increase network robustness. For example, multiple perceived receive attempts are created with no additional overhead. The system can be configured whereby nodes “hear” the transmissions of both adjacent and non-adjacent nodes forming implicit acknowledgement (“Acks”), and originating nodes can retransmit until implicit acknowledgments (“Acks”) are “heard,” indicating a successful link relay. Implicit acknowledgment can be applied to bidirectional networks, and bidirectional action can enable all nodes in the network to know the status of all other nodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority in U.S. Patent Application Ser. No.61/799,588 for Robust Network Downhole Telemetry Repeater System andMethod, filed Mar. 15, 2013, and is related to U.S. Patent ApplicationSer. No. 61/731,898 for Downhole Low Rate Linear Repeater Network TimingControl System and Method, filed Nov. 30, 2012, and No. 61/800,063 forHigh Throughput Downhole Telemetry Network System and Method, filed Mar.15, 2013. All of these applications are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to telemetry apparatuses andmethods, and more particularly to robust networks for downhole telemetryrepeater systems and methods for well drilling, production andcompletion, e.g., in the oil and gas and in other industries.

2. Description of the Related Art

Acoustic telemetry is a method of communication used in well drilling,production and completion. Applications include, but are not limited to,the oil and gas industry. In a typical drilling environment, acousticextensional carrier waves from an acoustic telemetry device aremodulated in order to carry information via the drillpipe as thetransmission medium to the surface. Upon arrival at the surface, thewaves are detected, decoded and displayed in order that drillers,geologists and others helping steer or control the well are providedwith drilling and formation data. In production wells, downholeinformation can similarly be transmitted via the well casings orproduction string. Acoustic telemetry transmits data to surface inreal-time and is independent of fluid flow, depth, well trajectory andother drilling parameters.

The theory of acoustic telemetry as applied to communication alongdrillstrings has generally been confirmed by empirical data in the formof accurate measurements. It is now generally recognized that the nearlyregular periodic structure of drillpipe imposes a passband/stopbandstructure on the frequency response, similar to that of a comb filter.Dispersion, phase non-linearity and frequency-dependent attenuation makedrillpipe a challenging medium for telemetry, the situation being madeeven more challenging by the significant surface and downhole noisegenerally experienced.

Drillstring acoustic telemetry systems are commonly designed withmultiple transceiver nodes located at spaced intervals along thedrillstring. The nodes can include repeaters. Acoustic telemetrynetworks can function in synch with the operation of the nodes andrepeater nodes and other system components. Data packets consisting ofdrilling operation data are relayed node to node in a daisy-chain/linearfashion, typically beginning from a node located in the boreholeapparatus (BHA), throughout the network to a destination, usually thesurface receiver system. For purposes of minimizing interference betweennodes, the data packets are transmitted (typically up-string) using timedivision multiplexing (TDM) techniques. Maximizing data packettransmission speed and throughput are objectives of drillstringtelemetry systems and methods. For a discussion of a repeater networkfor these applications, see co-pending U.S. Patent Application Ser. No.61/731,898, which is incorporated herein by reference.

When exploring for oil or gas, and in other well drilling, wellcompletion and energy resource production operations, an acoustictransmitter is preferentially placed near the BHA, typically near thedrill bit where the transmitter can gather certain drilling andgeological formation data, process this data, and then convert the datainto a signal to be transmitted, e.g., up-hole or in another direction,to an appropriate receiving and decoding station. In some systems, thetransmitter is designed to produce elastic extensional stress waves thatpropagate through the drillstring to the surface, where the waves aredetected by sensors, such as accelerometers, pressure transducers, etc.,attached to the drillstring or associated drilling rig equipment. Thesewaves carry information of value to the drillers and others who areresponsible for steering the well. Examples of such systems and theircomponents are shown in: Drumheller U.S. Pat. No. 5,128,901 for AcousticData Transmission through a Drillstring; Drumheller U.S. Pat. No.6,791,470 for Reducing Injection Loss in Drill Strings; Camwell et al.U.S. Pat. No. 7,928,861 for Telemetry Wave Detection Apparatus andMethod; and Camwell et al. U.S. Pat. No. 8,115,651 for Drill StringTelemetry Methods and Apparatus. These patents are incorporated hereinby reference.

The link performance within an acoustic repeater network is determinedby the signal-to-noise ratio (SNR) and level of channel distortion. Thelinks within a drillstring acoustic network are subject to largevariations in channel distortion and noise that cause the occasionalloss of signal packets. This loss represents a degradation in thenetwork performance as quantified in average data throughput. The largenoise variance means that the network performance remains degraded fromfull potential, even when average link quality is high. As the number ofthe nodes increases, the probability of lost packets increasesexponentially according to the generalized formula:

P _(Success) _(—) _(Network)=(P _(Success) _(—) _(Link))^(#Links)

where P_(Success) _(—) _(Network) is the probability of delivering apacket successfully throughout the network, P_(success) _(—) _(Link) isthe probability of delivering a packet successfully across a single linkin the network, and #Links is the number of inter-node communicationlinks within the network.

Increasing the link SNR, either through increased transmitter power orreduced node spacing, can improve network performance. However, this iscostly and lost packets, while reduced, will continue to persist onaccount of the large variation in noise and distortion.

SUMMARY OF THE INVENTION

In the practice of an aspect of the present invention, a robust networkis provided for exploiting the repeater structure of data propagation toavoid problems with transmitting data packets, which can be caused bysevere noise and distortion periods. Data packets typically containsensor or node status data and are transmitted from the primary node(e.g., ST0, typically the deepest node) and relayed from node-to-node ina daisy-chain (linear) fashion to the surface receiver (Surface Rx) 21,which is generally located at or near the wellhead. The data packetsinclude sensor measurements from the BHA 20 and other sensors along thedrillstring 12. Such data packet sensor measurements can include,without limitation, wellbore conditions (e.g., annular/bore/differentialpressure, fluid flow, vibration, rotation, etc.). Local sensor data canbe added to the data packet being relayed at each sensor node, thusproviding along-string-measurements (ASMs).

Network operation is typically managed through a time divisionmultiplexing channel management scheme, where node transmissions arescheduled for separate non-overlapping time windows. See co-pending U.S.Patent Application Ser. No. 61/800,063 for Increased Throughput DownholeNetwork Telemetry System and Method, which shows the operation of arepeater scheduling configuration using Time Division Multiplexing (TDM)channel management, and is incorporated herein by reference.

In the practice of an aspect of the present invention, a robust networkis provided. Severe noise and distortion periods tend to be relativelyshort in duration, whereby transmissions subsequent to a failure arelikely to succeed. Inter-node link success (e.g., network performance)can be improved through exploiting the time diversity properties of TDMand varying drillstring acoustic environment. For example, transmissionscan be repeated in hopes that retransmissions will occur in a morefavorable, reduced noise and distortion environment, but this method isrelatively inefficient. In the practice of an aspect of the presentinvention, the repeater structure of data propagation is exploited toincrease reception without incurring additional overhead. One solutionis therefore utilizing time diversity inherent in the reception oftransmissions from adjacent and non-adjacent nodes in a time divisionmultiplexing network for lessening the probability of packet loss.Another solution involves: implicit acknowledgment for the acousticdrillstring channels.

Other objects, advantages and aspects of the present invention will beapparent from the following description. Detailed descriptions ofexemplary embodiments are provided in the following sections. However,the invention is not limited to such embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a typical drilling rig, which can include anacoustic telemetry system, which can be equipped with a robust repeaternetwork embodying an aspect of the present invention.

FIG. 2 is a fragmentary, side-elevational and cross-sectional view of atypical drillstring, which can provide the medium for acoustic telemetrytransmissions for the present invention.

FIG. 3 is a schematic diagram of a system with nodes redundantlyreceiving messages multiple times for improved network robustness andperformance.

FIG. 4 is a schematic diagram of a system using implicit acknowledgmentwith an acoustic drillstring channel and an acoustic tool, both of whichare bi-directional.

FIGS. 5A and 5B show a schematic diagram of a bi-directional networkusing implicit acknowledgment.

FIG. 6 is a schematic diagram of a bi-directional network wherein allnodes are informed of the status of all other nodes (possibly forreliable confirmation of network configuration change command prior totransitioning between incompatible network configurations, alleviating arisk of lost nodes).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, reference is made to “up” and “down”waves, but this is merely for convenience and clarity. It is to beunderstood that the present invention is not to be limited in thismanner to conceptually simple applications in acoustic communicationfrom the downhole end of the drillstring to the surface. It will bereadily apparent to one skilled in the art that the present inventionapplies equally, for example, to subsurface stations, such as would befound in telemetry repeaters, and to other systems.

I. Drilling Rig, Drillstring and Well Environment

Referring to the drawings in more detail, the reference numeral 2generally designates a high throughput repeater system embodying anaspect of the present invention. Without limitation on the generality ofuseful applications of the system 2, an exemplary application is in adrilling rig 4 (FIG. 1). For example, the rig 4 can include a derrick 6suspending a traveling block 8 mounting a kelly swivel 10, whichreceives drilling mud via a kelly hose 11 for pumping downhole into adrillstring 12. The drillstring 12 is rotated by a kelly spinner 14connected to a kelly pipe 16, which in turn connects to multiple drillpipe sections 18, which are interconnected by tool joints 19, thusforming a drillstring of considerable length, e.g., several kilometers,which can be guided downwardly and/or laterally using well-knowntechniques.

The drillstring 12 can terminate at or near a bottom-hole apparatus(BHA) 20, which can be at or near an acoustic transceiver node (Primary)Station 0 (ST0). Other rig configurations can likewise employ thepresent invention, including top-drive, coiled tubing, etc. FIG. 1 alsoshows the components of the drillstring 12 just above the BHA 20, whichcan include, without limitation, a repeater transceiver node 26 (ST1)and an additional repeater transceiver node 22 (ST2). An upper, adjacentdrillpipe section 18 a is connected to the repeater 22 and thetransmitter 26. A downhole adjacent drillpipe section 18 b is connectedto the transmitter 26 and the BHA 20. A surface receiver node 21 islocated at the top of the drillstring 12 and is adapted for receivingthe acoustic telemetry signals from the system 2 for further processing,e.g., by a processor or other output device for data analysis,recording, monitoring, displaying and other functions associated with adrilling operation.

FIG. 2 shows the internal construction of the drillstring 12, e.g., aninner drillpipe 30 within an outer casing 32. Interfaces 28 a, 28 b areprovided for connecting drillpipe sections to each other and to theother drillpipe components, as described above. W.1 illustrates anacoustic, electromagnetic or other energy waveform transmitted along thedrillstring 12, either upwardly or downwardly. The drillstring 12 caninclude multiple additional repeaters 22 at intervals determined byoperating parameters such as optimizing signal transmissions withminimal delays and errors. The drillstring 12 can also include multiplesensors along its length for producing output signals corresponding tovarious downhole conditions.

Data packets contain sensor or node status data and are transmitted fromthe primary node (e.g., ST0, typically the deepest node) and relayedfrom node-to-node to the surface receiver (Surface Rx) 21, which isgenerally located at or near the wellhead. The data packets includesensor measurements from the BHA 20 and other sensors along thedrillstring 12. Such data packet sensor measurements can include,without limitation, wellbore conditions (e.g., annular/bore/differentialpressure, fluid flow, vibration, rotation, etc.). Local sensor data canbe added to the data packet being relayed at each sensor node, thusproviding along-string-measurements (ASMs).

A single node functions as the master node (e.g., ST0) and is typicallyan edge node at the top or bottom of the drillstring 12. The master nodemonitors well conditions and sends data packets of varying type andintervals accordingly.

As noted above, network performance problems are associated with lostdata packets, which can be caused by SNR and channel distortionvariances and are compounded with increasing numbers of nodes within thenetwork.

II. Solution 1: Exploiting Relay Network Time Diversity

As the acoustic drillstring channel is bidirectional and the acoustictransmitter can be configured to be bi-directional, transmissions of anode will propagate both uphole and downhole. The repeater structure ofdata propagation can be exploited to increase perceived attempts with noadditional overhead. FIG. 3 shows a system configuration whereby nodeswill “hear” the transmissions of both adjacent (“N+/−1”) as well asnon-adjacent nodes (“N+/−2”, “N+/−3”, etc.) Nodes can benefit from thetime diversity associated with the reception of transmissionsoriginating from adjacent and non-adjacent nodes, thus lessening theprobability of packet loss due to short-term noise/channel events.

A node will have multiple receipts of the same message, with varyingquality, and can: 1) choose the resulting data of best quality to berelayed; or 2) coherently combine the signals to enhance the SNR andrecover higher quality data for relaying. The quality of received datacan be determined through SNR and other waveform quality measures of thereceived packets, and/or the results from signal detection and errorcorrection algorithms (e.g., CRC, Hamming, convolutional encoding,etc.).

This system adds redundancy into the system, improving robustness byautomatically bridging intermittent or failed nodes, by recovering dataand network timing from the reception of non-adjacent transmissions,without the need for inter-node control signaling or other inefficientoverhead. Network robustness can therefore be increased with theaddition of nodes. This system is applicable to both upward (uplink) anddownward (downlink) directional networks, and is further applicable toEM repeater networks as well as acoustic networks.

III. Implicit Acknowledgment

FIG. 4 shows an alternative aspect of the present invention usingimplicit acknowledgment and bidirectional transmissions. As the acousticdrillstring channel is bidirectional and the acoustic transmitter can beconfigured to be bi-directional, node transmissions will propagate bothuphole and downhole. A node within an acoustic network will thereforehear the relay transmission of the above node(s). If a node isconfigured to only transmit in response to a successfully receivedpacket, receiving the “relay” transmission from the destination nodewill be therefore an implicit acknowledgment (“Ack”) of a successfullink relay. If the relay is not “heard,” the originating node canre-transmit until an implicit Ack is received, indicating successfulreceipt. This is useful in the case of critical data packets such ascontrol/error/configuration/alarm packets. Alternatively, theoriginating node can gather statistical information on the link successrate (e.g., percentage of successful transmissions) and accordingly takeone or more actions to improve network performance, conserve batterypower, or increase data rate: e.g., altering transmit power; alteringbaud rate; altering modulation; and/or altering frequency.

This method is passive in nature and requires no channel resources otherthan those required in the re-transmission. The onus for reliability ison the transmitting node, rather than the receiving node, removing thechallenging problem of detecting a missed message within a networkpropagating unpredictable messages types. Should the surface, or edgenode be configured to or not capable of repeating, the adjacent node inthe network will not receive implicit Acks. To handle this case, thesystem can be designed such that the adaptive link is enabled only uponreceipt of implicit Acks, indicating there it is no longer the lastlink. Nodes are inserted into the drillstring as the drillstring islowered into the wellbore (“tripping in”), nodes will be inserted beforesignal is completely lost, ensuring that Acks are received. The implicitacknowledgment system is applicable to both upward (uplink) and downward(downlink) directional networks, and is also applicable to EM repeaternetworks as well as acoustic networks.

In additional to providing feedback of successful link transmission, therelay transmission can be further exploited to provide an efficientmeasure of the inter-node acoustic channel to the transmitter. Thereceived relay transmission is largely composed of known data, havingbeen previously originated by the transmitter, which can be exploited toderive a measure of the channel response (e.g. frequency response). Asthe acoustic channel is reciprocal in nature, this channel measureinformation can be used to optimize transmission parameters to furtherimprove link robustness, throughput and efficiency. Transmissionparameters would include: total transmit power, transmit powerallocation across frequency (pre-equalization), baud rate, modulation,and error correction scheme. This method is of particular value tomulti-carrier modulation schemes, such as OFDM, in which channel measureinformation can be used to maximize bandwidth usage through subcarrierpower allocation and subcarrier modulation order.

The implicit channel measure method is applicable to both upward(uplink) and downward (downlink) directional networks, and is alsoapplicable to EM repeater networks as well as acoustic networks.

IV. Bidirectional Network

FIGS. 5A and 5B show a bidirectional network, which can optionallyutilize the implicit acknowledgment configurations and techniquesdescribed above. The bidirectional network shown in FIGS. 5A and 5Bexploits the inherent bidirectional transmission of signals transmittedon a drillstring or other structure. Payloads are prefixed with “U” forpropagation upwards to surface (uplink), and prefixed with “D” forpropagation downwards (downlink). Utilizing implicit acknowledgment,successful link relays can be acknowledged via Acks on the bidirectionalnetwork, similar to the previously described uplink only configurations.More specifically, for every uplink traversal through the full network(packet/update delivered to surface), a downlink-allocated payloadtraverses a single node link, i.e., high-latency downlink+low-latencyuplink/low-latency downlink+high-latency uplink. Bidirectional networkaction can thus be protected. Moreover, robustness and reliability ofthe network can be increased without adding additional overhead.

V. Bidirectional Network: Status

FIG. 6 shows an alternative aspect of the present invention with abidirectional network status configuration whereby bidirectional actioncan provide a mechanism for all nodes in the network to know the statusof all of the nodes. Payload can be added by every node, and can includedata and/or status. Data packet space can be allocated for a statusindication for each node in the network. This status payload is labeledin FIG. 6 with an “S” prefix. ST0 would relay its status to ST1, whereST1 would relay ST1's status along with its own status to the highernode, which in turn would do the same. The ST1 packet however is alsoreceived downhole by ST0 on account of the bi-directional nature of thetransmitter and channel, enabling ST0 to receive the status of ST1.Subsequent network updates to surface, higher station status wouldeventually be relayed down to the lower stations. All nodes are therebyinformed that all of the status of all other nodes. This provides ameans to provide confirmation of receipt throughout the network. Onesuch application being the reliable transition of the network betweenincompatible network configurations with a downlink command fromsurface. In this application, a transition would only be initiated onceall nodes have received indication that all other nodes have received acommand. Without the proposed scheme, a node failure to receive thetransition command would result in the loss of a node, degraded networkperformance or complete network failure.

It is to be understood that the invention can be embodied in variousforms, and is not to be limited to the examples discussed above. Therange of components and configurations which can be utilized in thepractice of the present invention is virtually unlimited.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:
 1. A telemetry repeater networksystem, which includes: multiple network nodes adapted for receiving andtransmitting data; a sensor associated with one or more of said nodesand adapted for providing output comprising signal data; and said systembeing configured whereby signals are received from both adjacent andnon-adjacent nodes.
 2. The telemetry network system according to claim1, which includes: said nodes being configured with a time divisionmultiplexing scheme for adjacent and non-adjacent transmissionreception; time multiplexing being defined as time windows allocated foradjacent and non-adjacent node transmissions; and said time multiplexingproviding a source of packet or data reception diversity, lessening theprobability of packet loss due to short-term noise and channel events.3. The telemetry network system according to claim 2 wherein: said nodeshave multiple receipts distributed over time of identical or similarsignal or data content packets, with varying quality; and the resultingdata of best quality is relayed; or signals are coherently combined toenhance signal-to-noise ratio (SNR) and recover higher quality data forrelaying to other nodes.
 4. The telemetry network system according toclaim 3 wherein: received data quality can be determined through asignal to noise ratio (SNR) measure of the received data packet and/orderived from an error detection and/or correction, signal detection orother quality encoding technique.
 5. The telemetry network systemaccording to claim 1 wherein: said system has added node redundancy forimproving robustness and network data net throughput; and said systemautomatically bridging intermittent or failed adjacent nodes via signalreception from non-adjacent nodes, without internode control signaling.6. The telemetry network system according to claim 1, which isapplicable to downhole drillstring networks comprising: uplink, downlinkand bidirectional networks; and acoustic and electromagnetic (EM)repeater networks.
 7. A telemetry repeater network system, whichincludes: multiple network nodes adapted for receiving and transmittingdata bi-directionally; a sensor associated with one or more of saidnodes and adapted for providing output comprising signal data packets;and said originating nodes determining successful reception by thedestination node via the successful reception of the destination node'ssubsequent relay packet, creating an implicit acknowledgement (Ack) ofsuccessful data packet reception.
 8. The telemetry network systemaccording to claim 7 which includes an originating node retransmitting adata packet until an implicit Ack is received, guaranteeing successfulreceipt.
 9. The telemetry network system according to claim 7, whichincludes: the formation of adaptive link management through anoriginating node gathering statistical information on the link successrate; and said originating node taking one or more of the followingactions to improve link robustness, conserve battery power or increasedata rate: altering transmit power; altering baud rate; alteringmodulation; altering error correction scheme; altering frequency;altering transmission medium; and altering power allocation ormodulation or error correction as function of frequency or subcarrier(in the case of multi-carrier formats).
 10. The telemetry network systemaccording to claim 9, which includes: the link success rate comprisingpercentage of successful transmissions, or ratio of successful tounsuccessful transmissions, possibly as a function of time.
 11. Thetelemetry network system according to claim 9 wherein said adaptive linkmanagement is without explicit control/feedback signaling that consumeschannel resources.
 12. The telemetry network system according to claim 9wherein: the adjacent t node to the destination node in the network willnot receive an implicit Ack; an adaptive link is enabled only uponreceipt of an implicit Ack, indicating that it is no longer the lastlink; and in the case of an expanding network, nodes being added to thenetwork before signal is lost, ensuring that Acks are received.
 13. Thetelemetry network system according to claim 7, which is applicable todownhole drillstring networks comprising: uplink, downlink andbidirectional networks; and acoustic and electromagnetic (EM) repeaternetworks.
 14. A bidirectional telemetry repeater network system, whichincludes: multiple network nodes adapted for receiving and transmittingdata bi-directionally; a sensor associated with one or more of saidnodes and adapted for providing output comprising signal data; for everyfull network relay, a downlink-allocated payload traverses a single nodelink; and said system has high latency/low throughput downlink and lowlatency/high throughput uplink or low latency/high throughput downlinkand high latency/low throughput uplink.
 15. The bidirectional telemetrynetwork system according to claim 14 wherein: said bidirectional actionprovides a mechanism for all nodes in the network to know the status ofall other nodes through natural bi-directional network relay action; andall nodes are informed that all other nodes have successfully received acommand permitting said system to achieve reliable transitions betweenincompatible network configurations in unison, thus alleviating risk ofloss nodes or network failure.
 16. The telemetry network systemaccording to claim 7 wherein said relay transmission provides a means tomake channel measures at the originating node without using additionalchannel resources or system overhead.
 17. The telemetry network systemaccording to claim 16, which includes the formation of adaptive linkmanagement through an originating node gathering channel information;and said originating node taking one or more of the following actions toimprove link robustness, improve net link data throughput, conservebattery power, or increase data rate: altering transmit power; alteringbaud rate; altering modulation; altering error correction scheme;altering frequency; altering transmission medium; and altering powerallocation or modulation or error correction as function of frequency orsubcarrier (in the case of multi-carrier formats).
 18. The telemetrynetwork system according to claim 16, wherein channel measures arefurther enabled through the inclusion of a known signal within relaypackets.
 19. The telemetry network system according to claim 14, whichis applicable to downhole drillstring networks comprising: uplink,downlink and bidirectional networks; and acoustic and electromagnetic(EM) repeater networks.
 20. A telemetry network system, which includes:multiple network nodes adapted for receiving and transmitting databi-directionally; a sensor associated with one or more of said nodes andadapted for providing output comprising signal data corresponding to anoperating or status condition; a transmitter associated with one or moreof said nodes for propagating said signal data between nodes; a receiverassociated with one or more of said nodes for receiving signals fromother nodes; said nodes providing an implicit acknowledgment (Ack) of adata packet for relay; and an originating node retransmitting a datapacket until an implicit Ack is received, indicating successful receipt.21. A telemetry network system, which includes: multiple network nodesadapted for receiving and transmitting data bi-directionally; a sensorassociated with one or more of said nodes and adapted for providingoutput comprising signal data corresponding to an operating or statuscondition; a transmitter associated with one or more of said nodes forpropagating said signal data between nodes; a receiver associated withone or more of said nodes for receiving signals from other nodes; anoriginating node retransmitting a data packet until an implicit Ack isreceived, indicating successful receipt; said Ack being applied tobidirectional networks; for every full network relay, adownlink-allocated payload traverses a single node link; and said systemhas high latency/low throughput downlink and low latency/high throughputuplink or low latency/high throughput downlink and high latency/lowthroughput uplink.